The
XtGetGC function returns a sharable, read-only GC. The parameters to this
function are the same as those for XCreateGC except that a widget is
passed instead of a display. XtGetGC shares only GCs in which all values
in the GC returned by XCreateGC are the same. In particular, it does not
use the value_mask provided to determine which fields of the GC a widget
considers relevant. The value_mask is used only to tell the server which
fields should be filled in with widget data and which it should fill in
with default values. For further information about value_mask and values,
see XCreateGC in the Xlib - C Language X Interface.